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3D internal wave focusing

Evgeny V. Ermanyuk, 18/10/2012

The talk presents an experimental study of internal waves emitted by a horizontally oscillating torus in a linearly stratified fluid. Internal waves are measured via precise tracking of distortions of horizontal fluorescein-dye planes created in the test tank prior to experiments and illuminated by a vertical laser sheet (Voisin et al (JFM 2011), Ermanyuk et al (JFM 2011)). This approach gives an access to the Lagrangian measurements of local wave amplitudes and slopes, in contrast with commonly used Eulerian-type techniques such as Synthetic Schlieren or PIV. The wave amplitudes in the converging wave system are strongly amplified in the focal region. Maximum wave slopes are found in the focal region and close to the surface of the torus. As the amplitude of oscillations of the torus increases, wave profiles in the regions of maximum wave slopes evolve non-linearly toward local overturning due to hydrostatic instability. Our observations support the theoretical scenario considered in Buhler & Muller (JFM 2007). The applicability of a quasi-2D approach to the description of the internal wave system close to the torus is discussed.